A very significant limitation on the operation and reliability of electronic devices is the efficient extraction of heat. Unless the devices are provided with an efficient heat transfer mechanism to maintain them within a predetermined operating temperature range, the speed, power, and useful life of the devices are severely limited. Excessive over-heating of electronic devices may cause their destruction.
The problem of heat removal from electronic circuit devices is increased when the devices are mounted on a thermally non-conductive substrate, such as an epoxy-glass printed circuit board. In a typical electronic module, the electronic devices are densely populated on the printed circuit board presenting a surface topology of varying heights, areas, and profiles.
It is a common approach in the cooling of heat generating electronic devices to provide each device requiring cooling with a poli-directional, or mono-directional localized heatsink. Thus, as shown in FIG. 1, an electronic module 10, includes a substrate 15 and heat generating devices 20 mounted on a surface 21 of the substrate 15. Heatsinks 30 are individually attached to the tops of the devices 20 for the purpose of dissipating heat. The drawbacks of such an approach is that the heatsinks 30 are of necessity limited in their footprints, must each be sized to conform to the geometry of the devices being cooled, must be aligned carefully with the device and are otherwise limited by the overall size of the system into which the module 10 is incorporated. It is tedious and expensive to adapt individually heatsinks to discrete heat generating devices which are diverse in placement and shape.
Alternatively, as shown in FIG. 2, heatsinks 30 have been provided for groups of localized devices 20 having similar dimensions. The main drawback of this approach is that it is a complex task to thermally mate the rigid heatsinks 30 with the devices 20. Generally, elastomeric compression pads, not shown, are required to ensure a good thermal contact between the heatsinks 30 and the devices 20. In addition, this method is not readily adaptable to multiple odd-shaped devices, and severely restricts the optimal layout of the devices 20 on the surface 21 of the substrate 15. Also, the relatively large weight of the assembled module 10 and the multiple screwholes required in the substrate 15 for attaching the heatsinks make this approach unattractive for mass-produced low-cost modules 10.
Yet another approach that has been used for cooling an electronic module 10 is shown in FIG. 3. In this arrangement a single heatsink 30 is in thermal contact with the opposite side of the substrate from the surface 15 on which the devices 20 are located. Although this scheme is fairly simple to assemble, it is less efficient in drawing heat from the devices 20 through the substrate 15, particularly if the devices 20 are surface mounted lacking leads protruding through the substrate 15 for conducting heat, or if the substrate 15 is made of a relative inexpensive material, for example, epoxy-glass, which has poor thermal conductive characteristics.
Accordingly, the known solutions for cooling an electronic module having varied heat generating devices mounted thereon increase the cost of assembly, and do not always provide for effective cooling of discrete and odd-shaped components.
Therefore, it is desirable to provide an apparatus and method for reliably cooling electronic modules with varied heat generating devices mounted thereon, which is simply to assemble, uses readily available inexpensive materials, and is easily adaptable to mass production methods.